Front-end systems using raster image memories for storing page data are known and used. Generally, they are used in printers which are capable of printing a complete page line-wise with serially presented data compared with on-the-fly systems, e.g., U.S. Pat. No. 4,031,519. A typical printer for complete page printing is the laser printer in which a light beam is modulated imagewise and deflected line-wise by means of a polygonal mirror over a light-sensitive surface. The latent image produced on the surface by the modulated light beam can be developed in a known manner and transferred to a receiving material such as a sheet of paper.
Graphical data, for example, may be obtained by scanning an image by means of a scanning device and storing the data, with or without the aid of a coding system, in a memory. The data for a page to be printed is first processed, for example by means of a graphical work station, to produce a finally desired layout which may contain textual and graphical data. If an assembled page has to be printed, the graphical information, coded or not coded, and the coded font data are fed to the front-end system along with information relating to height, width and finally desired position. In addition, the bit-map information of the characters to be printed is fed to the front end.
After the front end has stored all of the data in memory, it is necessary to set this data at the correct location in a page-size raster image memory or bit-map memory. The raster image memory is then serially read out and the data are fed to the modulator of the laser printer.
In the raster image memory, the bit representation of type characters and graphical characters is stored at a location which corresponds to the position which the character will finally attain on the printed page. Because modern laser printers are capable of printing pages at high speed and high resolution, the front-end system has to be capable of processing the data pages at high speed for presentation to the printer. For this purpose, the raster image memory will also have to fulfill the requirement imposed above. Accordingly, it is an object of the present invention to provide a raster image memory which can process the data needed for high-resolution printers at high speed.